Return of Antares expected to target August launch with OA-5 Cygnus

Orbital ATK’s continuing preparations to return its Antares rocket to flight operations has resulted in an updated preliminary launch date in the August timeframe. The launch – involving the OA-5 Cygnus spacecraft to the International Space Station (ISS) – requires static fire test data analysis to be completed, along with final trajectory shaping work.Antares Return:

According to Orbital ATK, in response to questions from NASASpaceFlight.com – the data review into the Static Fire is currently ongoing.

“We are continuing to prepare for the upcoming launch of the Antares rocket and Cygnus spacecraft for the OA-5 cargo logistics mission to the International Space Station from NASA’s Wallops Flight Facility. Our Antares team recently completed a successful stage test and is wrapping up the test data analysis,” noted the company.

Additional information pointed to data on “vibrations” during the Static Fire test that could be deemed as a problem for the vehicle’s avionics. A “fix” was already understood to have been approved.

Orbital ATK, while admitting the launch is slipping from its early July launch date estimate to a date likely to be in the August timeframe, pointed to trajectory evaluations as a specific relation to the launch date deliberations.

“Our Cygnus spacecraft for the OA-6 mission successfully undocked from the space station and hosted the Spacecraft Fire Experiment-I (Saffire),” added Orbital ATK. “The team is now performing the final OA-6 mission milestones.”

The first stage was set to burn for four minutes and 15.5 seconds before its engine shut down.

However, the timing of engine shutdown was shown to be six seconds earlier than planned.

Following staging, the Centaur’s RL10C-1 engine entered its prestart phase. Ten seconds after stage separation, the Centaur engine ignited to begin a single burn that was pre-planned for a duration of thirteen minutes and 38 seconds.

However, this burn lasted over a minute longer, as Centaur worked to overcome the shortfall of the Atlas V’s first stage performance.

Centaur ably delivered Cygnus into the correct 230km orbit and into its correct RAAN (Right Ascension of the Ascending Node), which ultimately classed the mission as a success.

The Upper Stage’s extra push resulted in Cygnus being 300 km further downrange than expected at spacecraft separation.

On Wednesday, ULA updated the status of its investigation into the Atlas V’s underperformance, caused by “an anomalous propellant mixture ratio resulting in an early booster shutdown and degradation of first stage performance.”

Citing a robust system design, flight software, vehicle margins and propellant reserves, the underperformance did not impact on the successful deployment of the Cygnus into her correct orbit.

This was thanks to the Centaur upper stage “identifying the first stage performance shortfall and compensated with an extended burn to deliver Cygnus to the precise orbit, well within the required accuracy,” as noted by ULA.

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The ULA engineering team, along with our engine supplier and several government customers, formed a review team that assessed all flight and operational data to determine direct and root causes and implemented the appropriate corrective actions for future flights.

“Thanks to the robust vehicle system design of Atlas V, the OA-6 mission was delivered successfully to its intended orbit and Cygnus completed its mission to the ISS,” noted Gary Wentz, ULA’s vice president of Human and Commercial Systems.

The imbalanced propellant consumption rate resulted in depletion of the first stage oxidizer with significant fuel remaining at booster engine shutdown.

In mitigation of this becoming an issue in the future, ULA noted that the engine supplier has implemented a minor change to the MRCV assembly. This change has been validated via “engine hot-fire testing, extensive component and assembly level testing and analyses.”

The final and corrective action reviews, as well as flight clearance for the Atlas V MUOS-5 mission occurred on June 2. The Atlas V MUOS-5 launch is scheduled for June 24 from Space Launch Complex-41 at Cape Canaveral.